A conventional compression refrigeration system such as air conditioning generally includes a compressor which compresses a vapor refrigerant to a high pressure and high temperature, a condenser which removes the latent heat of condensation causing the gas to condense to a liquid, a capillary tube which provides a restriction for reducing the pressure, and an evaporator which absorbs heat from the medium to be cooled thereby causing the liquid refrigerant to evaporate back into a gas.
The capillary tube has the advantage of being inexpensive, but has the disadvantage of being fixed. That is, the outlet pressure from the capillary tube is a function of the inlet pressure. In systems using air as the condensing medium, and to a lesser extent in those systems which use water, the temperature of the condenser varies as the temperature of the condensing medium varies. For example, on hot afternoons, the condenser temperature and thus its pressure increases thereby increasing the pressure to the inlet of the capillary tube, increasing the temperature and pressure from the outlet of the capillary tube causing refrigerant gas going to the compressor to be at a higher pressure and therefore more dense and causing the compressor to pump more pounds of refrigerant thereby further increasing the condenser pressure and further compounding the build up of pressure problem. One of the features of the present invention is the provision of an improvement for self regulating the refrigerant flow through the capillary tube for overcoming the buildup of the pressure cycle by means of the heat exchange from hot liquid to flash gas. Otherwise, carried to its extreme conclusion, pressure cycle buildup will cause loss of efficiency, overloaded equipment, safety trip outs and equipment failures.
Another problem with conventional systems is that while the system can be satisfactorily charged with refrigerant under factory conditions, it is difficult under field conditions to obtain an accurate charging of the refrigeration system with the refrigerant. Another feature of the present invention is the provision of an improvement in a refrigeration system which allows service personnel to more accurately charge the refrigeration system in the field with the correct amount of refrigerant.
Another problem with conventional systems is to provide compensation for refrigerant density which is dependent upon several variables. The present invention provides an improved system for establishing and storing a reserve capacity of refrigerant in the system and an improved means for allowing the service personnel to determine the amount of the reserve refrigerant which should be placed in the system.